[Devoxx Belgium '18] Things I wish I knew when I started building Android Libraries/SDK -Vol.2

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OSS Android libraries developed

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Android ARchive(AAR) @nisrulz

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AAR = Java ARchive(JAR) + Resources @nisrulz

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AAR = Java ARchive(JAR) + Resources @nisrulz Sensey: https://github.com/nisrulz/sensey

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AAR = Java ARchive(JAR) + Resources @nisrulz

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Using an AAR as dependency @nisrulz

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Using an AAR as dependency @nisrulz repositories{ flatDir{ dirs 'libs' } } dependencies { implementation(name:'nameOfYourAARFileWithoutExtension', ext:'aar') }

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Using an AAR as dependency @nisrulz repositories{ flatDir{ dirs 'libs' } } dependencies { implementation(name:'nameOfYourAARFileWithoutExtension', ext:'aar') } // None of the dependencies of the library are downloaded

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Why doesn’t my AAR download transitive dependencies? @nisrulz

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Sensey’s build.gradle @nisrulz dependencies { ... // Other testing dependencies // Transitive dependency: Support Compat library implementation "com.android.support:support-compat:27.0.2" }

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Sensey’s AAR @nisrulz

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Sensey’s AAR @nisrulz No build.gradle file

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Maven Artifact @nisrulz

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@nisrulz Maven Artifact

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POM? @nisrulz

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POM @nisrulz + Stands for Project Object Model + Is a XML file + Contains + Information about the project + Configuration details used by Maven to build the project

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POM @nisrulz POM of Sensey Android Library 4.0.0 com.github.nisrulzsensey1.8.0 aarsensey Android library which makes playing with sensor events & detecting gestures a breeze. https://github.com/nisrulz/sensey The Apache Software License, Version 2.0http://www.apache.org/licenses/LICENSE-2.0.txt nisrulzNishant [email protected] https://github.com/nisrulz/sensey.git https://github.com/nisrulz/sensey.git https://github.com/nisrulz/sensey com.android.support support-compat27.0.2 runtime ...

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POM @nisrulz POM of Sensey Android Library ... com.android.support support-compat27.0.2 runtime ...

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Bundled Proguard Configs @nisrulz

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Bundled Proguard Configs @nisrulz android { release { minifyEnabled true // Rules to be used during the AAR generation proguardFiles 'proguard-rules-for-building-library.pro' // Rules appended to the integrating app consumerProguardFiles 'proguard-rules-for-using-library.pro' } ... }

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Bundled Proguard Configs @nisrulz Fuel: https://github.com/kittinunf/Fuel

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Bundled Proguard Configs @nisrulz

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Bundled Proguard Configs @nisrulz # Fuel’s bundled Proguard file # Without specifically keeping this class, # callbacks on android don't function properly. -keep class com.github.kittinunf.fuel.android.util.AndroidEnvironment

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Bundled Proguard Configs @nisrulz # To check the merged configuration # Add the below to your current config -printconfiguration proguard-merged-config.txt

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Bundled Proguard Configs @nisrulz # DON'T DO THIS -dontobfuscate -optimizations !code/allocation/variable # Effectively no optimizations -keep public class * { public protected *; }

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Bundled Proguard Configs @nisrulz # DON'T DO THIS # Adding the below in library proguard rules disables # the optimizations in the Android app -dontoptimze

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Modularization @nisrulz

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Modularization @nisrulz

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Modularization @nisrulz EasyDeviceInfo: https://github.com/nisrulz/easydeviceinfo

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Modularization @nisrulz dependencies { def libVer = {latest_version} // Base + Ads Bundled Library implementation "com.github.nisrulz:easydeviceinfo:$libVer" // Base Library implementation "com.github.nisrulz:easydeviceinfo-base:$libVer" // Ads Library implementation "com.github.nisrulz:easydeviceinfo-ads:$libVer" }

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Modularization @nisrulz ... com.github.nisrulz easydeviceinfo-ads 2.4.1 compile com.github.nisrulz easydeviceinfo-base 2.4.1 compile ...

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Modularization @nisrulz ... com.github.nisrulz easydeviceinfo-ads 2.4.1 compile com.github.nisrulz easydeviceinfo-base 2.4.1 compile ...

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Modularization @nisrulz ... com.github.nisrulz easydeviceinfo-ads 2.4.1 compile com.github.nisrulz easydeviceinfo-base 2.4.1 compile ...

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Modularization @nisrulz ... com.github.nisrulz easydeviceinfo-common2.4.1 compile com.google.android.gms play-services-basement11.8.0 runtime ...

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Modularization @nisrulz ... com.github.nisrulz easydeviceinfo-common2.4.1 compile com.google.android.gms play-services-basement11.8.0 runtime ...

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Avoiding Resource Name Conflicts @nisrulz

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@nisrulz Conflict occurs between a library & app resource > Project will not compile What happens when..

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@nisrulz Conflict occurs between 2 libraries integrated in the app > Resources from library defined first in build.gradle gets included What happens when..

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@nisrulz Add a prefix to all your resources. Solution?

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@nisrulz Add a prefix to all your resources. Enforce this in Android Studio android { resourcePrefix 'YOUR_PREFIX_' // i.e 'sensey_' } Solution?

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@nisrulz Solution? Resource named ‘app_name’ does not start with the project’s resource prefix ‘sensey_’; Rename to `sensey_app_name`?

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minSdkVersion Restriction @nisrulz

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@nisrulz minSdkVersion of app >= minSdkVersion of library minSdk Restriction

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@nisrulz minSdk Restriction

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@nisrulz Manifest merger failed : uses-sdk:minSdkVersion 14 cannot be smaller than version 21 declared in library [:sensey] Suggestion: + Use a compatible library with a minSdk of at most 14 + Increase this project's minSdk version to at least 21 + Use tools:overrideLibrary="com.github.nisrulz.sensey" to force usage (may lead to runtime failures) minSdk Restriction

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@nisrulz ... minSdk Restriction

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@nisrulz ... minSdk Restriction

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Access Visibility vs Code Organization @nisrulz

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Visibility vs Organization @nisrulz + Code organized in individual packages; everything is public

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Visibility vs Organization @nisrulz + Code organized in individual packages; everything is public + Code organized inside one package; everything is package private and only public on demand

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Visibility vs Organization @nisrulz + Code organized in individual packages; everything is public + Code organized inside one package; everything is package private and only public on demand But if in Kotlin land, + Code organized in individual packages; everything is internal and only public on demand

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Visibility vs Organization @nisrulz // file name: exampleLibrary.kt // module name: example package com.example.library

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Visibility vs Organization @nisrulz // file name: exampleLibrary.kt // module name: example package com.example.library // visible inside exampleLibrary.kt private fun setup() { ... }

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Visibility vs Organization @nisrulz // file name: exampleLibrary.kt // module name: example package com.example.library // visible inside exampleLibrary.kt private fun setup() { ... } // property is visible everywhere public var name: String = "ExampleLib" // setter is visible only in exampleLibrary.kt private set{...}

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Lifecycle-Aware Android Library @nisrulz

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Lifecycle Components @nisrulz Classes designed to help deal with Android lifecycle + Lifecycle + LifecycleOwner + LifecycleObserver

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Lifecycle Components @nisrulz Classes designed to help deal with Android lifecycle

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Lifecycle Components @nisrulz Classes designed to help deal with Android lifecycle i.e Activity, Fragment, Service, Custom

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LifecycleObserver @nisrulz dependencies { def lifecycleVer = "1.1.1" // Runtime implementation "android.arch.lifecycle:runtime:$lifecycleVer" // Annotation Support annotationProcessor "android.arch.lifecycle:compiler:$lifecycleVer" ... }

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LifecycleObserver @nisrulz object AwesomeLibrary : LifecycleObserver { @OnLifecycleEvent(Lifecycle.Event.ON_CREATE) fun init() { ... } @OnLifecycleEvent(Lifecycle.Event.ON_START) fun onStart() { ... } ... @OnLifecycleEvent(Lifecycle.Event.ON_DESTROY) fun cleanup() { ...} }

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LifecycleOwner @nisrulz class MainActivity : AppCompatActivity() { // LifecycleOwner override fun onResume() { // Add lifecycle observer lifecycle.addObserver(AwesomeLibrary.INSTANCE) } override fun onStop() { // Remove lifecycle observer lifecycle.removeObserver(AwesomeLibrary.INSTANCE) } }

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ProcessLifecycleOwner @nisrulz Class that tracks the lifecycle of whole application process

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ProcessLifecycleOwner @nisrulz dependencies { def lifecycleVer = "1.1.1" // For ProcessLifecycleOwner implementation "android.arch.lifecycle:extensions:$lifecycleVer" ... }

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ProcessLifecycleOwner @nisrulz extension artifact automatically adds element to your manifest

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ProcessLifecycleOwner @nisrulz ...

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ProcessLifecycleOwner @nisrulz // Source code // Internal class to initialize Lifecycles. public class ProcessLifecycleOwnerInitializer extends ContentProvider { @Override public boolean onCreate() { ... ProcessLifecycleOwner.init(getContext()); return true; } ... }

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ProcessLifecycleOwner @nisrulz Initializes ProcessLifecycleOwner even if your app does not use it! Why? To invoke ProcessLifecycleOwner as soon as process starts

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Auto Initialize Android Library @nisrulz

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AutoInit Android Library @nisrulz Android Libraries need Android context to handle simple tasks such as + Hook into Android Runtime + Access app resources + Use System Services + Register BroadcastReceiver

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AutoInit Android Library @nisrulz public class MyApplication extends Application { @Override public void onCreate() { super.onCreate(); // Init android library MyAwesomeLibrary.init(this); } }

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AutoInit Android Library @nisrulz public class MyApplication extends Application { @Override public void onCreate() { super.onCreate(); // Init android library MyAwesomeLibrary.init(this); } }

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AutoInit Android Library @nisrulz public class MyApplication extends Application { @Override public void onCreate() { super.onCreate(); // Init android library MyAwesomeLibrary.init(this); } }

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AutoInit Android Library @nisrulz

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AutoInit Android Library @nisrulz ContentProvider “can be” used to simplify the process. How? ContentProvider is + Created and initialized (on the main thread) before all other components + Participate in manifest merging at build time.

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AutoInit Android Library @nisrulz public class AwesomeLibInitProvider extends ContentProvider { ... @Override public boolean onCreate() { // get the context (Application context) Context context = getContext(); // initialize AwesomeLib here AwesomeLib.getInstance().init(context); return false; } ... }

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AutoInit Android Library @nisrulz

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AutoInit Android Library @nisrulz

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AutoInit Android Library @nisrulz

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AutoInit Android Library @nisrulz

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AutoInit Android Library @nisrulz ContentProvider “can be” used to simplify the process. Why it shouldn’t be + There can be only one Content Provider with a given “authority” string + Only run on main thread; does not support multi process

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Links/References @nisrulz Android Libraries I have built: https://github.com/nisrulz/nisrulz.github.io#open-source-co ntributions Auto initialize android library example: https://github.com/nisrulz/android-examples/tree/develop/Au toInitLibrary Lifecycle Aware android library example: https://github.com/nisrulz/android-examples/tree/develop/Li feCycleCompForLib